1. Field of the Invention
The present invention relates to an ink-jet printing apparatus and an ink-jet printing method. More specifically, the invention relates to an ink-jet printing apparatus and an ink-jet printing method performing printing by ejecting an ink and a printing ability improving liquid which reacts with the ink to make the ink insoluble or coagulated.
2. Description of the Related Art
Associating with the spread of copy machines, information processing devices, such as word processor, computers and the like, and communication devices, printing apparatus performing digital image printing employing a head of an ink-jet system as one of image forming (printing) apparatus for these devices, are also spreading. In such printing apparatus, it is typical to employ a head having a plurality of ink ejection openings and liquid passages in high density, as a print head that integrates a plurality of printing elements in a high density array, for improving printing speed and to employ a plurality of such heads adapting to color printing.
FIG. 1 shows an example of construction of a printing portion employing the foregoing head for performing printing on a printing paper. In FIG. 1, reference numerals 701 denote ink cartridges, in which color inks of four colors of black, cyan, magenta and yellow are stored. To the ink cartridges 701 of respective colors, ink-jet heads 702 respectively corresponding to the ink cartridges are connected. The ink-jet heads 702 are mounted on a carriage 706 together with the ink cartridges 701.
A plurality of ink ejection openings arranged on the ink-jet head 702 as viewed from ink ejecting direction is illustrated in FIG. 2. In FIG. 2, the reference numeral 801 denotes the ink ejection opening. The ink ejection openings 801 are aligned in parallel to a Y-axis. The arrangement direction of the ejection opening may be slightly angled on XY plane in the drawing. In this case, while the head 702 is scanned in the traveling direction X, ejection may be performed from respective ejection openings with shifted timing. While the example shown in FIG. 1 arranges all of heads for four colors in scanning direction, the arrangement of the heads is not limited to the shown one. For instance, the four heads may be aligned in Y direction as paper feeding direction. Also, it is possible to arrange only one or two heads for one or two colors in the paper feeding direction.
Returning to FIG. 1, the reference numeral 703 denotes a paper feed roller rotating together with an auxiliary roller 704 in directions shown by arrows for feeding a printing paper 707 in the y direction at a predetermined timing. The reference numerals 705 denotes a pair of paper supply rollers performing supply of the printing paper, and in conjunction therewith, serving to flatten the printing surface of the printing paper 707 by applying a tension force on the printing paper 707 by a difference of rotation speed from that of the rollers 703 and 704. As set forth above, a carriage 706 mounts four ink-jet heads 702 and ink cartridges 701 and can move to perform scanning of the heads during printing operation. In conjunction therewith, at a non-printing state or upon performing an ejection recovery operation or the like for the head, the carriage 706 may be moved into a home position h as illustrated by broken line in FIG. 1. It should be noted that a structure of a cap or the like for performing the ejection recovery operation may be per se known in the art, and thus is not illustrated for simplification of illustration and disclosure.
The carriage 706 is located at the home position before initiation of printing and is responsive to a print start command to move in x direction in the drawing. During moving of the carriage in the x direction, ink ejection is performed through the ejection openings 801 of the head 702 depending upon printing data for performing printing over a width D (see FIG. 2) on the printing surface. Once printing for one scanning cycle is completed, at which the carriage 706 reaches end of the printing paper, the carriage 706 is returned to the home position for repeating similar scanning cycles. Bi-directional printing may be performed instead of uni-directional printing described above. During an interval between each scanning cycle, the paper feed roller 703 is driven to rotate for feeding a paper an amount corresponding to the width D. Thus, per each scanning cycle of the carriage, printing for the width D of the ejection opening array of the head and paper feeding are alternately repeated to complete printing for one page.
In ink-jet printing apparatus as set forth above, there is a progressively increasing demand for forming a color image on a plane paper, in the recent years. Even in this case, comparable image quality as that printed on a dedicated printing medium has been substantially achieved. However, when a water-base ink is employed, water-resistance of the image is insufficient so that storing ability is low.
As a measure for the problem set forth above, Japanese Patent Application Laid-Open No. 58-128862 (1983) discloses a technology to overlay the ink and a processing liquid effective for fixing the ink by ejecting the processing liquid before or after formation of the image of dots by ejection of the ink. Also, Japanese Patent Application Laid-Open No. 64-63185 (1989) discloses a technology for forming a dot by ejecting the ink after deposition of a compound which makes a dye in the ink insoluble. Furthermore, Japanese Patent Application Laid-Open No. 5-202328 (1993) discloses a method of depositing a processing liquid for fixing the ink providing water-resistance, by ejecting on the printing medium by ink-jet system, in advance of a dot forming operation, a method of depositing the processing liquid on the printing medium by roller application, and a method of improving fixing ability and water-resistance of the ink by mixing the ink and the processing liquid during flying as ejected from an ejector and depositing on the printing medium. Also, in order to avoiding excessive consumption of the processing liquid, commonly owned Japanese Patent Application Laid-Open No. 8-52867 (1996) discloses a technology for printing the processing liquid for improving fixing ability and water-resistance of the ink at a predetermined ratio relative to each pixel. Further, in Japanese Patent Application Laid-open No. 9-226154 (1997), attention is paid particularly to an edge portion of the image. In a region other than the edge portion of the image, the processing liquid is ejected at a predetermined ratio, whereas, on the edge portion of the image, the processing liquid is ejected to avoid consumption of an extra amount of the processing liquid to certainly provide water-resistance. Furthermore, commonly owned Japanese Patent Application Laid-open No. 8-104000 (1996) discloses a method for controlling the kind of an appropriate processing liquid and the ejection amount depending upon the peripheral environment of the printing apparatus and kind of the printing medium.
It should be noted that the foregoing processing liquid is effective not only for improving water-resistance of the printed image but also for enhancing density, preventing bleeding and feathering, and the like. In view of these effects, the processing liquid may also be referred to as a printing ability improving liquid.
However, in any of the prior arts set forth above, a manner, an amount and so on of ejection of the processing liquid were handled similarly either in the case where one ink droplet is ejected for one pixel or in the case where the two or more droplets are ejected for one pixel. Therefore, under certain circumstance, water-resistance in the mixed color portion may become insufficient. This problem will be more specifically explained hereinafter.
FIGS. 3A to 3D show four patterns of a head construction including a processing liquid ejection head and of deposition of the ink droplet and the processing liquid on the printing medium. FIG. 3A shows a construction, in which respective heads 702Bk, 702C, 702M and 702Y for black (Bk), cyan (C), magenta (M) and yellow (Y) and a head 702S for the processing liquid (S) are arranged in a scanning direction. FIG. 3B shows a construction, in which a head 702col in which ejection openings for cyan, magenta and yellow are arranged in the paper feeding direction, the black head 702Bk and the processing liquid head 702S are arranged. FIG. 3C shows a construction, in which the heads for respective colors are arranged in similar manner to that of FIG. 3A but dedicated processing liquid heads 702S, 702Sm, 702Sc and 702Sk are arranged adjacent to respective of corresponding color heads. FIG. 3D shows a construction, in which a head 702INK having ejection openings for Y, M, C and Bk are aligned in paper feeding direction and the processing liquid head 702S are arranged in the scanning direction.
When these four kinds of head constructions are employed, there are various deposition states of the ink droplet and the processing liquid droplet, namely various manner of printing methods, depending upon construction of respective head array and manner or the like of generating the processing liquid ejection data. Respective examples are shown on the right sides of respective of FIGS. 3A to 3D. These figures illustrate examples of forming a green (C+Y) image.
FIGS. 3A and 3C show depositing condition formed by scanning at once. On the other hand, FIGS. 3B and 3D show deposition condition formed by two scanning times between which paper feeding operation is inserted.
Further, as a manner of generation of the processing liquid ejection data, deposition conditions shown in FIGS. 3A and 3B are cases where the processing liquid ejection data is generated by deriving a logical sum of ejection data of Y and C. On the other hand, deposition conditions shown in FIGS. 3C and 3D are the case where the processing liquid ejection data is generated corresponding to respective ejection data of Y and C.
The amount of the processing liquid necessary for making the ink insoluble or coagulated is differentiated depending upon composition of respective color inks, ejection amount, number of ink droplets to be ejected for one pixel and the like. Accordingly, it is not always required to eject one processing liquid droplet for one ink droplet.
On the other hand, among ejection data generation methods shown in FIGS. 3A to 3D, the methods shown in FIGS. 3A and 3B are the ones for generating the processing liquid ejection data by logical sum of respective colors of ejection data, only one processing liquid droplet is ejected even when a plurality of ink droplets are ejected for one pixel. Therefore, sufficient processing liquid as required may be not ejected with respect to the ink. Accordingly, in the case of printing by a primary color, while water-resistance or the like is sufficient, water-resistance or the like can be insufficient for the case of printing of secondary color or more, in which a plurality of colors of inks are overlaid.